EMERGENCY services will hone their preparations for terrorism when they respond to a mock shooting involving dozens of people today.

The National counter-terrorism exercise, code named Mercury 10, is scheduled for Rymill Park from 9am.

A police spokeswoman said all emergency services would be involved.

"Mercury 10 begins with a mock terrorist attack that involves a shooting with dozens of casualties in Rymill Park," the spokeswoman said. The action moves to Mile End this afternoon and ends at the Islington rail yards this evening.

Last week SA Police letter dropped 13,000 residents who may be affected by the exercise.

Parking is restricted on Bartels Rd for the duration of the exercise for use by emergency vehicles.----------------------------------------Interesting pager messages on the website.